^0.5 is broken for LanguageClient-neovim, likely others

First, thanks for this language server. It’s awesome and I look forward to it becoming even more awesome.

Problem

A combination of changes between 0.4.1 and 0.5.0 broke compatibility with my LSP client (LanguageClient-neovim, latest version, commit hash ee6cdb0940d9c2c95f31488f7d463b2d12abcbc4. Using neovim 0.5.0 dev). I suspect it’s broken for other Vim/neovim clients as well.

Error with yaml-language-server version ^0.5

“Cannot read property 'hierarchicalDocumentSymbolSupport' of undefined”

Plethora of problems

Line 351 of src/server.ts contains the following line:

hierarchicalDocumentSymbolSupport = !!capabilities.textDocument.documentSymbol.hierarchicalDocumentSymbolSupport;

This errors out when the server capabilities does not contain a documentSymbol. The LSP specification allows a client to omit this information, but the yaml-language-server does not elegantly handle this case (hierarchicalDocumentSymbolSupport is called on the undefined “documentSymbol” attribute).

I tried updating this line to:

hierarchicalDocumentSymbolSupport = !!(capabilities.textDocument.documentSymbol && capabilities.textDocument.documentSymbol.hierarchicalDocumentSymbolSupport);

But now I receive a new error:

[LC] [Error] Notification handler 'workspace/didChangeConfiguration' failed with message: workspaceFolders is not iterable

Therefore, the remedy is more complex than simply catching the “undefined” case.

Full original error message

WARN unnamed src/language_server_protocol.rs:2217 Failed to start language server automatically. Error: Failure { jsonrpc: Some(V2), error: Error { code: InternalError, message: "Request intialize failed with message: Cannot read property \'hierarchicalDocumentSymbolSupport\' of undefined", data: None }, id: Num(1) }

Evidence from coc.nvim

Coc’s yaml extension pins this library to 0.4.0, which strengthens my suspicion that yaml-language-server is broken for other vim language clients; coc users wouldn’t notice the breakage because they don’t use the latest version.

https://github.com/neoclide/coc-yaml/blob/master/package.json

  "dependencies": {
    "yaml-language-server": "^0.4.0"
  }

Reference

• Specification section on Initialization

[bollwyvl]

Perhaps something as blunt as:

    workspaceFolders = params.workspaceFolders || [];

    try {
        hierarchicalDocumentSymbolSupport = !!capabilities.textDocument.documentSymbol.hierarchicalDocumentSymbolSupport;
    } catch { }

    try {
        clientDynamicRegisterSupport = !!(capabilities.textDocument.rangeFormatting && capabilities.textDocument.rangeFormatting.dynamicRegistration);
    } catch { }

[JPinkney]

I’ve just released 0.6.0 which contains these fixes!